Reproduction/ Sex steriod axis Flashcards
what 2 gonadotrophic hormones are secreted by the pituitary gland
FSH and LH
what does FSH do in males
causes the testes to produce sperm
what does FSH do in females
causes the growth of ovarian follicles (oogenesis) and causes the ovary to secrete oestrogen
what does LH do in males
causes the testes to secrete testosterone
what does LH do in females
causes ovulation and progesterone production by the corpus luteum
how does testosterone affect levels of LH, FSH and GnRH
when high will reduce the levels of LH and FSH and GnRH by negative feedback HPG axis
what is the HPG axis
hypothalamus - anterior pituitary - LH and FSH - ovaries (oestrogen and progesterone) and testes (testosterone)
what hormone causes the release of FSH and LH from the anterior pituitary
gonadotrophin releasing hormone GnRH)
what type of hormone if GnRH and what makes and releases it
neuropeptide hormone
made and released by GnRH neurones within the hypothalamus
how is GnRH released in both males and females
in a pulsatile manner
what is the different between GnRH secretion in males and females
males- constant pulses
females- frequency of pulses varies depending on menstrual cycle (1-2 hours during early follicular phase, decreasing to 4 hours during luteal phase)
what do high frequency GnRH pulses stimulate
LH pulses
what do low frequency GnRH pulses allow
FSH release
how does oestrogen affect GnRH
high oestrogen (above 200) will increase GnRH pulsatility driving the release of LH
below 200 reduces frequency of GnRH pulses (FSH release)
why is modulation of LH pulse frequency needed
for pubertal maturation and reproductive function
what happens to GnRH in the onset of pubertal maturation
steady acceleration i GnRH pulsatility (peak at night- boys causes peak in testosterone in morning, erections)
what are the signs of delayed puberty
no period by age of 15
boys no sign of testicular development by age 14
how is GnRH pulsatility regulated
GnRH neurones activated by kisspeptin as dont have receptors for oestrogen and progesterone (the hormonal regulators)
what is the variable part of the menstrual cycle
follicular (proliferative phase) typically 14 days +/- 7 days
what is the follicular phase characterised by
follicular growth
what is the more constant phase of the menstrual cycle
luteal phase (secretory phase)
what causes the LH surge
when high oestrogen causes positive feedback
why does FSH cause an increase in oestrogen
as follicles produce oestrogen
what does LH surge causes
ovulation, regulates the formation of the corpus luteum, progesterone production and secretion (from follicle)
how does increasing progesterone affect LH
decreases LH secretion by influencing GnRH pulsatility
what does increasing progesterone do to LH secretion
decreases it by influencing GnRH pulsatility
what hormone dominates the luteal phase
progesterone
what makes up a follicle
an oocyte surrounded by folicular cells (granulosa cells, theca cells)
happens happens to the follicle during its growth
increase in the number of follicular cells and accumulation of follicular fluid (increases in diameter and size)
what effect does oestrogen have on the endometrium
thickens
what effect does progesterone have on the endometrium
causes it to become a secretory tissue
what hormone stimulates follicular growth
FSH (granulosa cells)
LH (theca cells)
what happens in follicular growth if there is a lack of FSH
build up of androgens
how many follicles in each ovary
7 million
2 million at birth
0.5 million at puberty
how can FSH determine if a follicle is lost or not
when reaches certain size follicle becomes gonadotrophin dependent (2-5mm), if this doesnt coincide with rise in FSH during early follicular phase then follicle is lost
how many follicles are selected for ovulation
1 (5/6 grow during each menstruation)
what can predict the timing of ovulation
the LH surge (precedes ovulation by 34-36 hours)
what happens to progesterone in LH surge
increases- essential for ovulation as stimulates enzymes that break down follicular wall releasing enzymes
what hormone causes the formation of the corpus luteum
LH
how do cells form the corpus luteum
granulosa and theca cells transform into luteal cells
how does LH cause the formation of the luteal corpus
stimulates angiogenesis (ensures delivery of cholesterol which is the synthesis for progesterone synthesis) stimulates enzymes involved in conversion of cholesterol to progesterone
what are the functions of oestrogens
increases the thickness of the vaginal wall
regulate the LH surge
reduce vaginal pH though increase in lactic acid production
decreased viscosity of cervical mucous to facilitate sperm penetration
what is the role of progesterone
maintains the thickness of the endometrium creates infertile thick mucous (prevents sperm and infection) relaxes myometrium (smooth muscle) important in maintaining pregnancy
what hormones control spermatogenesis
LH and FSH and testosterone
how long does spermatogenesis take
70 days
what makes up the testes
seminiferous tubules surrounded by interstitial tissue
what is in the intratubular compartment of the testes
sertoli and germ cells
where does spermatogenesis take place
in the seminiferous tubules in the testes
what is in the seminiferous tubules
sertoli cells and maturing germ cells surrounded by peritubular myoid cells
what cells are stimulated by FSH to start spermatogenesis
sertoli cells
what receptors do leyid cells (in testes) have
LH receptors- when bound secrete testosterone
what paracrine factors affect spermatogenesis
testosterone and inhibin
what is the role of testosterone in spermatogenesis
maintains the blood testes barrier
causes the release of mature spermatozoa from sertoli cells by influencing peritubular myoid cells
